This invention relates generally to electrostatographic reproduction machines, and more particularly to an environmentally friendly "green" rapid recovery fusing apparatus in such a machine.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith.
Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roller or to a latent image on the photoconductive member. The toner attracted to a donor roller is then deposited on a latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate or sheet. The copy substrate or sheet carrying the powder image is then moved to a heat and pressure fusing apparatus, for example, where the toner powder particles are heated in order to fuse and permanently affix them to the copy substrate or sheet.
As is well known, when started up, each reproduction machine typically goes through a warm up phase during which the heated member of the fusing apparatus gradually warms up to where the fusing channel or fusing nip reaches and can be maintained at the high fusing temperature. After that, the machine can be activated to run a job reproducing images through a run or operating cycle. After one of such jobs, the machine may be idle (or even go into an idle or a "standby" mode), while waiting for the next reproduction job. Conventionally, an efficiency practice as disclosed for example in U.S. Pat. No. 4,920,250 has been to turn off the power supply upon entering a idle or standby mode, and to allow the temperature of the fusing nip or channel to drop to, and to then be controlled by restarting and shutting off the power supply, at a lower temperature level.
Consistent with such a conventional practice, environmentally sensitive and market place regulations, now call for office equipment, particularly electrostatographic reproduction machines, to be more energy efficient. Such environmental regulations or requirements for office products are covered in the US under what is currently called the "Energy Star Program", and under various other similar programs in Europe and elsewhere. Such similar programs include "New Blue Angel" (Germany), "Energy Conservation Law" (Japan), "Nordic Swan" (North Europe), and "Swiss Energy Efficiency Label" (Switzerland).
Under the "Energy or Power Star Program" in the United States, several modes are defined for copiers or electrostatographic reproduction machines. These modes for example include the operating or copying mode, the standby mode, and the low-power or energy-saver mode. The low-power or energy-saver mode is the lowest power state a copier can automatically enter within some period of copier inactivity, without actually turning off. The copier enters this mode within a specified period of time after the last copy was made. When the copier is in this mode, there may be some delay before the copier will be capable of making the next copy. For purposes of determining the power consumption in this low-power mode, a company may choose to measure the lowest of either the energy-saver mode or the standby mode.
Responsible Corporations have committed to implementing "Green" concepts in their products, and are planning to have as many products as possible receive an "Energy Star" award/classification. As part of this, guidelines for their products include provisions for an energy saver mode, in which power consumption is allocated and limited. For example, in mid volume toner reproduction machines, the power allocated is limited 150-200 watts.
The copier or machine enters the standby mode when it is not in the operating or copying mode making copies, but had just previously been in the operating mode. In the standby mode, the copier or machine is consuming less power than when the machine is in the operating mode but is ready to make a copy, and has not yet entered into the energy-saver mode. When the copier is in the standby mode, there will be virtually no delay before the copier is back in the operating mode and capable of making the next copy.
When the machine is in the low-power or energy-saver mode, these regulations call for the total power being consumed by the machine to be limited to no more than 125 watts, of which no more than 50 watts can be to the fusing apparatus. When the copier or machine experiences prolonged low-power or energy-saver mode periods, this level of limited power (50 watts) to the fusing apparatus usually is only sufficient to maintain the temperature of the fusing apparatus at a temperature that is significantly below the desired high and ready-to-run fusing temperature of about 350 degrees Fahrenheit.
Timely and satisfactory recovery from such a significantly low low-power or energy-saver mode temperature back to the desired high fusing temperature is ordinarily difficult. This is because once the temperature of a fusing apparatus starts to drop or fall, it acquires a thermal inertia which then makes reversal or recovery difficult. Unfortunately, the "power or energy star" regulations, have made such a concern a problem for conventionally designed and controlled fusing apparatus, by calling for the reproduction machine to fully recover from such a low-power or energy-saver mode temperature back up to the desired, high fusing temperature in 30 seconds or less. Under conventional practice, recovery times have been found to be unacceptably long and beyond the 30 seconds called for by the regulations.